1. Field of the Invention
The present invention relates to an adjusting arrangement for a hydraulic pump with a variable flow quantity, having an operating cylinder located in a neutral position through the intermediary of a positively-acting resetting device, the piston of which is adjustable dependent upon the actual discharge pressure and dependent upon a parameter proportional to the actual discharge flow quantity into a position corresponding to the rated discharge flow quantity with consideration being given to the limiting value for maximum power output, maximum discharge pressure, maximum discharge flow quantity and, as required, the flow direction; and with an electronic control arrangement which receives electrical signals corresponding to the rated discharge flow quantity and the actual discharge flow quantity and the actual pressure, which processes these signals under calculation of the actual power output and the actual pressure, and generates corresponding setting signals for the adjustment of the operating cylinder.
Hydraulic pumps with adjustable discharge quantities are, in general, equipped with mechanical or electromechanical adjusting arrangements. By means of these the hydraulic pumps should be correlated with the present purpose of the utilization, whereby there are to be maintained the limits with regard to the maximum discharge flow quantity, the maximum discharge pressure, as well as the maximum power output. The power output of a hydraulic pump is determined through N-discharge flow quantity multiplied by the discharge pressure. Within the plane of the discharge quantity/discharge pressure there is accordingly produced a hyperbola. The range of the power achievable through the hydraulic pump is restricted by the parameters (compare with FIG. 3), wherein this is applicable to both discharge flow directions. For the practical case of application this signifies that within the pump operating circuit there must be provided an adjusting arrangement which restricts the maximum permissible pressure of the pump. The maximum possible discharge flow quantity of the pump is limited through the discharge volume thereof and the permissible rotational speed. At a given discharge flow quantity, the operating pressure of the hydraulic pump can thus be raised up to the power output curve. When a hydraulic pump is to be operated at a constant power output, then the discharge flow quantity must be correspondingly varied by means of the adjusting arrangement.
2. Discussion of the Prior Art
For the operation of the pump within the mentioned power output range there has become known an adjusting arrangement of the above-mentioned type from German Laid-open Patent Application 23 13 853. The known adjusting arrangement contains an impact plate system in which the impact plate is adjusted in conformance with a rated value, whereby the adjustment is effected through an electrical calculator which considers the actual discharge pressure and the limiting value for discharge flow quantity. The discharge flow quantity-actual/rated-value comparison is effected pneumatically in such a manner that the two chambers of the operating cylinder presently power one nozzle whose jets impinge against the impact plate. The maximum value of the discharge pressure is given consideration through a safety relief valve. Thus there is contended that this adjustment can also be effected in an electrical mode, however, it is not indicated as to how that type of an electrical adjustment can be achieved. It is disadvantageous in the known adjusting device that there must be effected an individual correlation of the essentially mechanical adjusting arrangement to the different constructional pump sizes, which means that, for each pump size, there must be provided its own adjusting arrangement and also correlated therewith. Constructional tolerances within a pump size can also not be taken into consideration. This means that the power output which stands available cannot be fully utilized. Any change in the power output curve in comparison with the maximum possible power output curve is not possible without an exchange of the mechanical arrangement. Thus, a precise reproducability for each hydraulic pump associated power curve is not possible.
In another known adjusting arrangement for a hydraulic pump with a variable discharge flow quantity as disclosed in German Laid-open Patent Application 20 45 405, the control of the adjustment of the piston within the operating cylinder is effected in an electrical manner through control of the electromagnets of a servovalve, however, the known adjusting arrangement is constructed only for the time-dependently controlled adjustment of the piston between its end positions. Through this adjusting arrangement the hydraulic pump can thus not be operated with a suitably preselectable power output.